High purity polycrystalline silicon is a material for a single crystal silicon substrate for producing a semiconductor device, or a material for producing a solar cell. Generally, high purity polycrystalline silicon is produced batch-wise by a method (Siemens method) for performing pyrolysis or hydrogen reduction of a silicon-containing reaction gas as a source gas into high purity silicon, and precipitating the high purity silicon on a thin silicon filament rod. The silicon-containing reaction gas includes gases such as monosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane, or a halogen gas generally represented by SiHnX4-n (n=0, 1, 2, 3; X=Br, I).
A general precipitation reaction container used for producing high purity polycrystalline silicon is constituted by a metallic bed plate (base plate) and a metallic bell jar placed on the base plate, and an inside of the bell jar is a reaction space. It is necessary that the precipitation reaction container can be cooled and can seal a gas in the bell jar. This is because the reaction gas described above is corrosive, and may cause ignition or explosion by mixture with air.
If precipitation reaction of polycrystalline silicon is performed in the precipitation reaction container, during a CVD process, amorphous silicon dust is formed by a homogeneous nucleation process, and silicon adheres to an inner surface of the precipitation reaction container. The silicon dust contains a high level contaminant, and is settled on polycrystalline silicon as a product to cause surface defect or contamination (see Patent Literature 1).
Since the precipitation reaction of polycrystalline silicon described above is performed batch-wise, the inner surface of the bell jar inevitably comes into contact with the atmosphere when the polycrystalline silicon is taken out from the bell jar. The silicon-containing reaction gas as a source gas and chlorosilanes or halogen gases obtained as by-products by the precipitation reaction remain on the inner surface of the bell jar after the precipitation reaction of polycrystalline silicon. It is known that such gases become highly corrosive when reacting with moisture in the atmosphere.
The corrosive gas described above expresses and activates hazardous substances (for example, boron, aluminum, phosphorus, arsenic, antimony) that reduce quality of polycrystalline silicon, from a structure member on the inner surface of the bell jar.
Such hazardous substances are taken into polycrystalline silicon during a precipitation reaction process for a next batch to reduce quality of the polycrystalline silicon (for example, see Patent Literature 2).
From such circumstances, a precipitation bell jar is washed using high purity water or a carbon dioxide pellet for each batch or every few batches to clean the inner surface.
Meanwhile, generally, an automated washing apparatus is used for a bell jar because of a large inner surface area or difficulty in wiping in terms of structure. Patent Literatures 1 and 2 mentioned above and Patent Literature 3 disclose such a washing apparatus and a washing method using the apparatus.